[build-script] XCTest CI builds on OS X
[build-script] XCTest CI builds on OS X

Fix the OS X XCTest CI preset:

1. Installation of XCTest isn't supported on OS X. After all, the
   library is meant to be used on Linux, and not intended to be used or
   installed on OS X. Therefore, no longer pass an `INSTALL_PATH` to the
   `xcodebuild` invocation on OS X.
2. `xcodebuild` expects `swift-stdlib-tool` to be present in the same
   directory as the `SWIFT_EXEC` it's given. Re-use some shellscript
   from the toolchain installation script to copy the stdlib-tool
   substitute.

This allows the XCTest CI to work on all platforms.

lorentey/swift,Jnosh/swift,natecook1000/swift,jtbandes/swift,natecook1000/swift,OscarSwanros/swift,glessard/swift,JaSpa/swift,bitjammer/swift,manavgabhawala/swift,hughbe/swift,IngmarStein/swift,KrishMunot/swift,rudkx/swift,ben-ng/swift,danielmartin/swift,ahoppen/swift,lorentey/swift,parkera/swift,kperryua/swift,brentdax/swift,stephentyrone/swift,manavgabhawala/swift,airspeedswift/swift,xwu/swift,zisko/swift,shajrawi/swift,gottesmm/swift,xwu/swift,jtbandes/swift,allevato/swift,ben-ng/swift,ahoppen/swift,shahmishal/swift,benlangmuir/swift,aschwaighofer/swift,jtbandes/swift,harlanhaskins/swift,practicalswift/swift,rudkx/swift,rudkx/swift,tinysun212/swift-windows,shahmishal/swift,benlangmuir/swift,IngmarStein/swift,gottesmm/swift,kstaring/swift,parkera/swift,tardieu/swift,atrick/swift,lorentey/swift,felix91gr/swift,codestergit/swift,frootloops/swift,CodaFi/swift,hooman/swift,ken0nek/swift,therealbnut/swift,benlangmuir/swift,shajrawi/swift,ken0nek/swift,parkera/swift,arvedviehweger/swift,lorentey/swift,jopamer/swift,swiftix/swift,benlangmuir/swift,tardieu/swift,glessard/swift,CodaFi/swift,codestergit/swift,CodaFi/swift,gribozavr/swift,kperryua/swift,johnno1962d/swift,xedin/swift,jopamer/swift,jmgc/swift,ben-ng/swift,shajrawi/swift,milseman/swift,tjw/swift,kperryua/swift,bitjammer/swift,harlanhaskins/swift,tkremenek/swift,gribozavr/swift,ahoppen/swift,OscarSwanros/swift,KrishMunot/swift,djwbrown/swift,milseman/swift,KrishMunot/swift,sschiau/swift,shahmishal/swift,zisko/swift,allevato/swift,jmgc/swift,russbishop/swift,IngmarStein/swift,natecook1000/swift,russbishop/swift,gribozavr/swift,ben-ng/swift,jtbandes/swift,modocache/swift,uasys/swift,manavgabhawala/swift,allevato/swift,huonw/swift,atrick/swift,airspeedswift/swift,IngmarStein/swift,allevato/swift,apple/swift,harlanhaskins/swift,gribozavr/swift,roambotics/swift,sschiau/swift,calebd/swift,devincoughlin/swift,tinysun212/swift-windows,apple/swift,amraboelela/swift,danielmartin/swift,atrick/swift,stephentyrone/swift,gmilos/swift,natecook1000/swift,allevato/swift,CodaFi/swift,bitjammer/swift,practicalswift/swift,gottesmm/swift,gregomni/swift,brentdax/swift,IngmarStein/swift,milseman/swift,tjw/swift,jmgc/swift,jckarter/swift,gmilos/swift,KrishMunot/swift,SwiftAndroid/swift,amraboelela/swift,karwa/swift,parkera/swift,gmilos/swift,shahmishal/swift,tardieu/swift,zisko/swift,tardieu/swift,milseman/swift,arvedviehweger/swift,allevato/swift,SwiftAndroid/swift,tinysun212/swift-windows,austinzheng/swift,jckarter/swift,manavgabhawala/swift,hughbe/swift,JGiola/swift,glessard/swift,jmgc/swift,hughbe/swift,return/swift,tkremenek/swift,practicalswift/swift,stephentyrone/swift,kperryua/swift,sschiau/swift,JaSpa/swift,IngmarStein/swift,tinysun212/swift-windows,allevato/swift,aschwaighofer/swift,uasys/swift,SwiftAndroid/swift,ken0nek/swift,tinysun212/swift-windows,russbishop/swift,OscarSwanros/swift,stephentyrone/swift,nathawes/swift,sschiau/swift,djwbrown/swift,huonw/swift,Jnosh/swift,sschiau/swift,roambotics/swift,calebd/swift,JGiola/swift,devincoughlin/swift,gottesmm/swift,russbishop/swift,glessard/swift,tjw/swift,lorentey/swift,johnno1962d/swift,amraboelela/swift,huonw/swift,alblue/swift,russbishop/swift,CodaFi/swift,swiftix/swift,amraboelela/swift,dreamsxin/swift,stephentyrone/swift,alblue/swift,manavgabhawala/swift,xedin/swift,brentdax/swift,swiftix/swift,felix91gr/swift,felix91gr/swift,calebd/swift,CodaFi/swift,alblue/swift,calebd/swift,kperryua/swift,kstaring/swift,gmilos/swift,sschiau/swift,djwbrown/swift,return/swift,return/swift,gregomni/swift,aschwaighofer/swift,modocache/swift,nathawes/swift,sschiau/swift,SwiftAndroid/swift,austinzheng/swift,jmgc/swift,karwa/swift,jtbandes/swift,calebd/swift,codestergit/swift,benlangmuir/swift,gmilos/swift,atrick/swift,manavgabhawala/swift,karwa/swift,stephentyrone/swift,djwbrown/swift,swiftix/swift,tjw/swift,brentdax/swift,milseman/swift,xedin/swift,xedin/swift,return/swift,gmilos/swift,ben-ng/swift,tkremenek/swift,bitjammer/swift,parkera/swift,ben-ng/swift,ken0nek/swift,hughbe/swift,johnno1962d/swift,gribozavr/swift,tardieu/swift,hooman/swift,bitjammer/swift,zisko/swift,frootloops/swift,djwbrown/swift,devincoughlin/swift,Jnosh/swift,huonw/swift,apple/swift,ken0nek/swift,JaSpa/swift,atrick/swift,uasys/swift,xwu/swift,devincoughlin/swift,swiftix/swift,deyton/swift,karwa/swift,roambotics/swift,lorentey/swift,alblue/swift,kstaring/swift,apple/swift,jckarter/swift,gregomni/swift,jopamer/swift,codestergit/swift,danielmartin/swift,frootloops/swift,xedin/swift,ben-ng/swift,JGiola/swift,danielmartin/swift,practicalswift/swift,roambotics/swift,return/swift,hughbe/swift,dreamsxin/swift,shahmishal/swift,JaSpa/swift,Jnosh/swift,atrick/swift,ahoppen/swift,hughbe/swift,shajrawi/swift,calebd/swift,tjw/swift,shahmishal/swift,huonw/swift,practicalswift/swift,jckarter/swift,airspeedswift/swift,jopamer/swift,CodaFi/swift,benlangmuir/swift,parkera/swift,KrishMunot/swift,tkremenek/swift,JGiola/swift,kstaring/swift,uasys/swift,SwiftAndroid/swift,swiftix/swift,glessard/swift,milseman/swift,gregomni/swift,swiftix/swift,karwa/swift,shajrawi/swift,practicalswift/swift,therealbnut/swift,djwbrown/swift,kstaring/swift,deyton/swift,natecook1000/swift,modocache/swift,gottesmm/swift,shajrawi/swift,tinysun212/swift-windows,OscarSwanros/swift,jopamer/swift,KrishMunot/swift,milseman/swift,xedin/swift,devincoughlin/swift,JGiola/swift,airspeedswift/swift,stephentyrone/swift,nathawes/swift,brentdax/swift,gribozavr/swift,hughbe/swift,gmilos/swift,OscarSwanros/swift,JGiola/swift,frootloops/swift,JaSpa/swift,jmgc/swift,xedin/swift,ken0nek/swift,arvedviehweger/swift,gottesmm/swift,arvedviehweger/swift,austinzheng/swift,devincoughlin/swift,bitjammer/swift,karwa/swift,amraboelela/swift,nathawes/swift,arvedviehweger/swift,djwbrown/swift,glessard/swift,johnno1962d/swift,tardieu/swift,shahmishal/swift,calebd/swift,uasys/swift,alblue/swift,therealbnut/swift,codestergit/swift,devincoughlin/swift,zisko/swift,zisko/swift,tinysun212/swift-windows,shahmishal/swift,jckarter/swift,harlanhaskins/swift,apple/swift,kperryua/swift,practicalswift/swift,arvedviehweger/swift,tkremenek/swift,gregomni/swift,therealbnut/swift,kperryua/swift,hooman/swift,harlanhaskins/swift,xedin/swift,amraboelela/swift,danielmartin/swift,jmgc/swift,kstaring/swift,arvedviehweger/swift,hooman/swift,SwiftAndroid/swift,codestergit/swift,codestergit/swift,deyton/swift,kstaring/swift,johnno1962d/swift,russbishop/swift,jckarter/swift,alblue/swift,ken0nek/swift,deyton/swift,uasys/swift,tjw/swift,gregomni/swift,natecook1000/swift,sschiau/swift,ahoppen/swift,shajrawi/swift,danielmartin/swift,hooman/swift,karwa/swift,alblue/swift,jtbandes/swift,danielmartin/swift,aschwaighofer/swift,modocache/swift,hooman/swift,jopamer/swift,ahoppen/swift,hooman/swift,deyton/swift,johnno1962d/swift,practicalswift/swift,therealbnut/swift,aschwaighofer/swift,therealbnut/swift,JaSpa/swift,amraboelela/swift,parkera/swift,xwu/swift,SwiftAndroid/swift,airspeedswift/swift,deyton/swift,brentdax/swift,felix91gr/swift,parkera/swift,huonw/swift,xwu/swift,shajrawi/swift,Jnosh/swift,airspeedswift/swift,gribozavr/swift,tardieu/swift,apple/swift,airspeedswift/swift,karwa/swift,austinzheng/swift,natecook1000/swift,nathawes/swift,harlanhaskins/swift,manavgabhawala/swift,bitjammer/swift,austinzheng/swift,johnno1962d/swift,aschwaighofer/swift,frootloops/swift,rudkx/swift,Jnosh/swift,tkremenek/swift,felix91gr/swift,aschwaighofer/swift,return/swift,JaSpa/swift,rudkx/swift,austinzheng/swift,OscarSwanros/swift,tkremenek/swift,frootloops/swift,KrishMunot/swift,jopamer/swift,roambotics/swift,devincoughlin/swift,rudkx/swift,Jnosh/swift,modocache/swift,frootloops/swift,jckarter/swift,modocache/swift,brentdax/swift,lorentey/swift,zisko/swift,nathawes/swift,nathawes/swift,huonw/swift,deyton/swift,austinzheng/swift,lorentey/swift,OscarSwanros/swift,harlanhaskins/swift,jtbandes/swift,gottesmm/swift,felix91gr/swift,uasys/swift,modocache/swift,roambotics/swift,IngmarStein/swift,xwu/swift,xwu/swift,tjw/swift,therealbnut/swift,felix91gr/swift,russbishop/swift,return/swift,gribozavr/swift